Circuit interrupters are electrical components that are used to open an electrical circuit, interrupting the flow of current. A basic example of a circuit interrupter is a switch, which generally consists of two electrical contacts in one of two states; either closed, meaning that the contacts are in electrical contact with each other allowing electricity to flow between them, or open, meaning that the contacts are not in electrical contact with each other preventing the flow of electricity. A switch may be directly manipulated to provide a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch.
Another example of a circuit interrupter is a circuit breaker. A circuit breaker is designed to protect an electrical circuit from damage caused by, for example, an overload, a ground fault or a short circuit. If a fault condition, such as a power surge occurs in the electrical wiring, the breaker will trip. This will cause a breaker that was in an “on” position to flip to an “off” position and interrupt the flow of electrical power through the breaker. Circuit breakers are generally provided to protect the electrical wiring by limiting the amount of current transmitted through the wires to a level that will not damage them. Circuit breakers can also prevent destruction of the devices that may draw too much current.
A standard circuit breaker has a first terminal connected to a source of electrical power, and a second terminal electrically connected to the wires that the breaker is intended to protect. Conventionally, these terminals are referred to as the “line” and “load”, respectively. The line is sometimes referred to as the input of the circuit breaker. The load is sometimes referred to as the output of the circuit breaker, which connects to the electrical circuit and components receiving the electrical power.
A circuit breaker can be used as a replacement for a fuse. Unlike a fuse, however, which typically operates to open in an over current situation and then must be replaced; a circuit breaker can be “reset” (either manually or automatically) to resume operation. Fuses perform a similar role to circuit breakers, however, circuit breakers are easier to use and typically safer to service and operate.
Unlike the situation when a fuse blows, when a circuit breaker trips, it is relatively easy to determine which circuit breaker feeds the interrupted circuit by looking at the electrical panel and noting which breaker has a handle in the “tripped” position. This breaker can then be simply moved to the “off” position (which resets the circuit breaker), and then moved to the “on” position and power will resume.
In general, a single pole circuit interrupter has at least two contacts positioned inside of a housing. The first contact is stationary and may be connected to either the line or the load. The second contact is movable with respect to the first contact, such that when the circuit breaker is in the “off” or “tripped” position, a gap exists between the first and second contact.
In high voltage applications, the opening and closing of contacts, can result in an arc developing between the contacts. High voltage applications typically are associated with high power transfer and therefore, the switching devices used in these applications must be able to effectively and safely switch even under load.
A problem with the above-described circuit interrupters arises when energized contacts are opened while under load. As the contacts separate, an electric arc may be formed in the gap between the contacts. An electrical arc is a plasma discharge between two points that is caused by electrical current that ionizes gasses in the air between the two points.
The creation of an arc during transition of the contacts can result in undesirable effects that negatively affect the operation of the circuit interrupter, even potentially creating a safety hazard. These negative effects can also have adverse consequences on the functioning of the circuit interrupter.
One possible consequence is that the arc may short to objects inside the circuit interrupter and/or to surrounding objects, causing damage and presenting a potential fire or safety hazard.
Another consequence of arcing is that the arc energy damages the contacts themselves, causing some material to escape into the air as fine particulate matter. The debris that has been melted off of the contacts can migrate or be flung into the mechanism of the circuit interrupter, destroying the mechanism or reducing its operational lifespan.
Still another effect of arcing is due to the extremely high temperature of the arc (tens of thousands of degrees Celsius), which can impact the surrounding gas molecules creating ozone, carbon monoxide, and other dangerous compounds. The arc can also ionize surrounding gasses, potentially creating alternate conduction paths.
The challenges faced in high voltage applications is further complicated with Direct Current (DC) applications as there is no zero voltage crossing. In Alternating Current (AC) applications, opening of the contacts can be timed to correspond with the zero voltage crossing to minimize potential arcing. However, in DC applications there is no zero voltage crossing; therefore switching must quite often happen at peak voltage under load.
It is therefore desired to provide a circuit interrupter usable in DC applications that overcomes the above-described limitations.